Discharge printing is a well known technique in the textile industry for the production of white and colored sharply outlined patterns which are characterized by close-fitting, fine details, and small motiffs on contrasting color (usually darker) ground shades. It is broadly known therefore that such designs may be produced by printing a discharge print paste in a desired pattern onto the darker-colored ground shade produced with a dyestuff which is dischargeable to white when the paste-printed textile material is subjected to high-temperature steaming so as to permit the discharge agent in the print paste to distroy the dyestuff in those areas of the print pattern. The use of dyestuffs which are resistant to the discharge agent in the print paste are also known so that when the ground shade is discharged to white, the discharge-resistant dyestuff (conventionally known as a "reservable dyestuff") remains as a visible contrasting color to the ground color.
With the advent of synthetic fiber textile materials, problems were encountered in discharging ground shades of disperse dyes which are fixed to the synthetic fibers (conventionally termed "fully dyed"). Accordingly, the discharge printing of synthetic textile materials, for example, polyesters, fully dyed with disperse dyestuffs presented significant problems to those in this art. Fully-dyed synthetic textile materials (i.e., those textile materials in which the dyestuffs are fixed or dissolved in the synthetic fibers) are resistant to attack by discharge agents in the aqueous discharge paste due to the highly crystalline structure and hydrophobic nature of the synthetic fibers, particularly, the polyesters.
To overcome this problem, the discharge print process was modified by first padding the textile material with a dye liquor containing a disperse dyestuff and then drying or superficially drying the material at temperatures so as to prevent fixation of the dyestuff in the synthetic fiber. A desired pattern could then be printed onto the textile material with the non-fixed dyestuff therein so that when the padded and printed fabric is subsequently subjected to high-temperature steaming, the dyestuff will be discharged to white in the pattern areas of the print paste prior to its fixation in the synthetic fibers. The high-temperature steaming concurrently causes the nonpattern areas of the dyestuff to be fixed in the synthetic fibers so that upon subsequent rinsing, a white pattern area or contrasting color pattern area (if a reservable dye is included in the ground dyestuff) results. In this regard, the reader's attention is directed to U.S. Pat. Nos. 3,972,677 and 4,252,530, the disclosure of each being expressly incorporated hereinto by reference.
The discharge printing method described immediately above whereby disperse dyestuffs are discharged prior to their fixation in the synthetic fibers of the textile material has been conventionally termed "discharge-resist printing" and this term will be utilized herein to distinguish it from the classical discharge printing technique whereby fully dyed fabrics with fixed dyestuffs are pattern printed with a discharge paste and then discharged via high temperature steaming.
Discharge-resist printing, however, while overcoming many disadvantages associated with discharge printing of synthetic textile materials in accordance with the classical discharge printing technique is not without problems of its own. For example, when discharge-resist printing is attempted to be utilized for light-weight synthetic fabrics (i.e., less than about 40 grams per square yard), shading problems occur due to mechanical difficulties encountered when ground shades are padded onto the fabric and to dyestuff migration during the superficial drying step which thus leads to an unsatisfactory textile product. Moreover, it is not easy to completely destroy or discharge the ground dyestuff even when it is not fixed in the synthetic fibers without the use of strong reducing agents or oxidizing agents. Use of strong reducing or oxidizing agents is disadvantageous since they also attack the synthetic fibers per se thereby prejudicing their use with light-weight synthetic fabrics. Moreover, heavy metal salts such as stannous chloride are typically used in discharge resist printing so as to completely destroy the ground dyestuff (see, U.K. Pat. No. 1,412,681 and U.K. Pat. No. 1,440,904). Use of stannous chloride however is very corrosive to processing equipment and results in heavy metal effluent disposal problems. Moreover, the use of stannous chloride as a discharge agent is typically restricted to the use of anthraquinone disperse dyestuffs when colored discharges are required and which are available commercially in much smaller numbers than the more plentiful azo disperse dyestuffs.
Alkali-dischargeable dyestuffs have also been proposed for use in the discharge resist printing techniques as described in, for example, U.K. Pat. No. 1,543,724 and U.S. Pat. No. 4,252,530, the disclosure of each being expressly incorporated hereinto by reference. Alkali dischargeable disperse dyestuffs having carboxylic acid ester groups of the type disclosed in U.K. Pat. No. 1,543,724 are, however, very sensitive to hydrolysis and require careful handling and strict control of pH and the use of sodium or potassium dichromate during processing which presents effluent disposal problems. Additionally, dyestuffs having carboxylic acid ester groups exhibit an affinity for nylon and hydrophilic natural fibers, such as cotton and rayon, after saponification of the ester groups during alkali treatment and thus tend to dye or stain these types of fibers causing so-called "halation" or the lowering of the sharpness of the pattern. Accordingly, such carboxylic acid ester group disperse dyes are typically not utilized to discharge print fabric blends of synthetic and natural fibers. In addition, diazo components and the coupling components required for the manufacture of dyestuffs containing carboxylic acid ester groups are specialty items thereby often times ruling out their use as being excessively expensive. Accordingly, only a very limited number of carboxylic acid ester group-containing disperse dyes is presently commercially available, namely CI disperse yellow 126, CI disperse orange 127, CI disperse red 278 and 311, CI disperse blue 284 and 288, CI disperse green 9 and CI disperse brown 19. * FNT The source of all color indices used herein is "Color Index", 3rd edition (1971).
Recently, it has been proposed that classical discharge printing of fully-dyed (i.e., fixed) lightweight polyester fabrics can be accomplished utilizing the carboxylic acid ester group-containing disperse dyestuffs of U.K. Pat. No. 1,543,724 in conjunction with a specially-formulated discharge paste which contains an alkali (preferably sodium hydroxide) together with a blend of ethoxylated products and polyols (i.e., Matexil PNAD and Matexil PN-DG, Imperial Chemical Industries PLC) as described in Brierley et al, "The Use of Disperse Dyes Containing Diester Groups to Produce Discharge Effects on Fully Dyed Lightweight Polyester Fabrics", JSDC, Vol. 99, pages 358-363 (Dec. 1983), the entire content thereof being expressly incorporated hereinto by reference. The alkali print paste proposed by Brierley et al however, appears to be suitable only for use with the carboxylic acid ester group-containing dyestuffs of the type described in U.K. Pat. No. 1,543,724 which, as indicated previously, are available in limited quantities and tend to be rather expensive due to their chemically special nature.
Utilizing the above discussion as a background, the reader will undoubtedly appreciate that discharge printing of a hydrophobic synthetic material to overcome the above disadvantages has been needed for some time.